linux-kernel - Re: [PATCH v12 1/1] vhost: Reintroduces support of kthread API and adds mode selection

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Message-ID: <6107dcb2-51a3-42f8-b856-f443c0e2a60d@6wind.com>
Date: Wed, 18 Jun 2025 14:06:30 +0200
From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
To: Cindy Lu <lulu@...hat.com>, jasowang@...hat.com, mst@...hat.com,
 michael.christie@...cle.com, sgarzare@...hat.com,
 linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH v12 1/1] vhost: Reintroduces support of kthread API and
 adds mode selection

Le 16/06/2025 à 08:28, Cindy Lu a écrit :
> This patch reintroduces kthread mode for vhost workers and provides
> configuration to select between kthread and task worker.
> 
> - Add 'fork_owner' parameter to vhost_dev to let users select kthread
>   or task mode. Default mode is task mode(VHOST_FORK_OWNER_TASK).
> 
> - Reintroduce kthread mode support:
>   * Bring back the original vhost_worker() implementation,
>     and renamed to vhost_run_work_kthread_list().
>   * Add cgroup support for the kthread
>   * Introduce struct vhost_worker_ops:
>     - Encapsulates create / stop / wake‑up callbacks.
>     - vhost_worker_create() selects the proper ops according to
>       inherit_owner.
> 
> - Userspace configuration interface:
>   * New IOCTLs:
>       - VHOST_SET_FORK_FROM_OWNER lets userspace select task mode
>         (VHOST_FORK_OWNER_TASK) or kthread mode (VHOST_FORK_OWNER_KTHREAD)
>       - VHOST_GET_FORK_FROM_OWNER reads the current worker mode
>   * Expose module parameter 'fork_from_owner_default' to allow system
>     administrators to configure the default mode for vhost workers
>   * Kconfig option CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL controls whether
>     these IOCTLs and the parameter are available (for distros that may
>     want to disable them)
> 
> - The VHOST_NEW_WORKER functionality requires fork_owner to be set
>   to true, with validation added to ensure proper configuration
> 
> This partially reverts or improves upon:
>   commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
>   commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
> 
> Signed-off-by: Cindy Lu <lulu@...hat.com>
> ---
>  drivers/vhost/Kconfig      |  17 +++
>  drivers/vhost/vhost.c      | 244 ++++++++++++++++++++++++++++++++++---
>  drivers/vhost/vhost.h      |  22 ++++
>  include/uapi/linux/vhost.h |  29 +++++
>  4 files changed, 294 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 020d4fbb947c..1b3602b1f8e2 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -95,4 +95,21 @@ config VHOST_CROSS_ENDIAN_LEGACY
>  
>  	  If unsure, say "N".
>  
> +config VHOST_ENABLE_FORK_OWNER_CONTROL
> +	bool "Enable VHOST_ENABLE_FORK_OWNER_CONTROL"
> +	default n
Why disabling this option by default?

Regards,
Nicolas